Turbomachine with reduced leakage penalties in pressure change and efficiency

ABSTRACT

A turbomachine is provided having at least one row of blades oriented at a predetermined stagger. Casing grooves are provided proximate to at least a portion of the tip of the blades. The grooves are oriented substantially normal to the stagger of the blades. The normal of the blade is determined from a chord of the blade. The chord may be taken across a pair of corresponding points one the upstream and downstream end of the blade, hence across the extent of the cross-sectional shape of the blade. Alternatively, a blade chord may be determined over only a portion of the blade, for instance, from a point along the centerline of the upstream end of the blade to a second point on the centerline midway down the blade from the upstream end. Optimally, the grooves are positioned adjacent to the upstream half of the blades, but may continue across the axial extent of the blades. The spacing between grooves can be optimized for blade stagger in order to find an optimal number of grooves that concurrently cross the blade. Additionally, obtaining an optimal groove depth for a particular turbomachine requires knowing only the tip clearance gap as groove depth is directly related to the tip clearance. Furthermore, since the groove may be substantially smaller than prior art casing treatments, fluid recirculation is reduced. The blade-normal groove may take a variety of cross-sectional shapes. Optimally, the aft surface of the groove will have less than a 45° incline to the radial at that point.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to turbomachinery. Moreparticularly, the present invention relates to casing treatments forincreasing the efficiency of fluid flow in a turbomachine.

2. Description of Related Art

In general, turbomachines utilize rows of blades on a hub (axle orwheel) that spin with respect to a stationary casing that encloses thehub and blades. Interleaved between the rows of rotating blades are rowsof stationary vanes (or blades) disposed on the casing wall. As usedherein internally, the terms blade, vane and airfoil will be usedsynonymously, although it is generally understood in the art that ablade is attached to the rotating hub or axle, while a vane is affixedto the stationary housing. The airfoil configuration of the blades isoriented on the hub at a precise angle, or stagger, with respect to theaxis of rotation of the machine; similarly, the vanes are also orientedon the casing wall at a precise stagger angle. A gap (clearance gap) isrequired between the tips of the blades and the stationary casing wallto avoid friction and prevent a catastrophic failure of the machine. Ablade or airfoil is generally considered to consist of two surfaces thatbound the blade passage. One surface largely faces the direction ofrotation while the other faces the opposite direction. The two surfacesmay be called “low” and “high” pressure surfaces of the airfoil, butwhich one corresponds surface facing the direction of rotation dependson whether the device is being used to increase the pressure of thefluid (compressor or pump) or being used to extract work from the fluid(turbine).

The following three directional definitions are commonly used whendiscussing turbomachinery. (1) Axial refers to the direction parallel tothe axis of rotation, pointing in the downstream direction. (2) Radialrefers to the direction orthogonal to the axis of rotation pointingoutward from the axis. (3) Tangential (also called circumferential)points in the direction of blade rotation.

The clearance gap is a source of tip leakage of fluid (gas for acompressor, liquid for a pump) between the high pressure side of theblades and the lower pressure side, i.e., in the relative frame ofreference of the blade passage fluid leaks circumferentially over thetips of the blades from the high to low pressure side of the airfoils.Viewed in the relative frame of the blade passage, it is widely knownthat the interaction between the tip leakage and main passage flowresults in loss (reduced efficiency) and reduced effective flow area(reduced pressure rise for compressor or pump) at the exit of thepassage. The main passage flow orientation that is largely parallel tothe airfoil surface in the relative frame of reference of the blade ishenceforth called the streamwise direction.

Historically, the focus of designers has been to minimize gap clearancein an effort to reduce the amount of leakage and thereby increase theefficiency of the turbomachine. These clearance-based approaches haveprimarily concentrated on mollifying two independent factors: dynamicstructural deformity and thermal expansion. For instance, the shape ofrotating blades deform as a result of the dynamic forces on the blades.The primary phenomena that dynamically affect the clearance are the“centrifugal” forces, thermal expansion, and frictional forces thatinteract on the blades. Centrifugal forces cause the rotor and blades toelongate, resulting in the blade tips being displaced radially outward,thereby reducing the clearance across substantially all of the bladetip. Fluid dynamic forces on the airfoil, on the other hand, cause theblades to deform axially and twist, thereby reducing the clearance ofthe blade tips away from the rotational axis of the airfoils. Theextreme operating conditions of a turbomachine in terms of pressure andtemperature also affect the shape of the casing wall.

Changes in temperature cause the rotor and blades to expand andcontract, but thermal expansion is generally unrelated to the dynamicforces. Some aircraft turbines experience temperature variations in theincoming air stream of over 150° F. (65.60° C.), for instance, betweenthe hot air on the tarmac and subfreezing air at cruising altitude andthese variations get magnified due to engine compression.

Many of the clearance-based approaches directed to counteracting dynamicstructural deformation of the rotor blades are devoted to decreasing thedensity (and weight) of the blades while simultaneously increasing theirstiffness. Thus, the magnitude of the centrifugal forces on the bladesis reduced resulting in a corresponding reduction in the resultingelongation of the blades caused by the centrifugal forces at higheroperating speeds. A myriad of techniques have been employed to achievethis result, such as adopting less dense, but stronger materials andconstruction techniques, including, but not limited to high performancealloys and innovative structural design. Innovative techniques areemployed to achieve favorable thermal expansions of the rotor, blades,and case.

Another technique used by designers for reducing leakages has been inthe area of abradable seal elements, which are designed, in general, toallow for minimal wear without experiencing a catastrophic failure. Someexamples of abradable seal elements are found in, for instance, U.S.Pat. No. 3,365,172 to McDonald, Jan. 23, 1968; U.S. Pat. No. 3,411,794to Allen, Nov. 19, 1968; U.S. Pat. No. 3,529,905 to Meginnis, Sep. 22,1970; U.S. Pat. No. 3,719,365 to Emmerson, Mar. 6, 1973; U.S. Pat. No.6,203,021 to Wolfla, Mar. 20, 2001; U.S. Pat. No. 6,830,428 to Le Biez,Dec. 14, 2004; U.S. Pat. No. 6,887,528 to Lau, May 3, 2005; and U.S.Pat. No. 7,029,232 to Tuffs, Apr. 18, 2006, which are incorporated byreference herein in their entireties. While the design concepts varybetween the specific applications, in general the sealing elementprovides an abradable sealing material on or in the casing surfaceregion and/or the blade tips. This material is sufficiently abradable orcrushable so that contact with the other parts, including blades, tips,ridges, or knives on the other members of the seal, will provide theclearance for rotation without damaging the other member of the seal ordestroying the effectiveness of the abradable part.

Still other techniques have been devoted to casing (or shroud)treatments which modify the flow in the tip region without using anabradate material. Typically, an air channel is formed in the casingwall proximate to at least a portion of the blade tip which disrupts thetip leakage or provides a path for energized downstream fluid (in thecase of a pump or compressor) to enter further upstream therebyenergizing the flow near the tip. The channel is generally oriented withrespect to the axis of rotation of the turbomachine, casing (or shroud)or hub without regard to the stagger of the blade. The geometry of priorart channels takes one of three general configurations: circumferential;axial; and recessed (passages). FIGS. 1A, 1B and 1C are diagrams of aportion of blade and casing wall with circumferential, axial andrecessed casing treatments as known in the prior art. In each diagram,rotating blade 104 is affixed to a rotating hub (not shown) with bladetip 106 proximate to and separated from stationary casing body 113 bygap (clearance) 110. Surfaces facing opposite rotation direction 109 andsurfaces facing rotation direction (not shown) of blade 104 areoptimally configured as airfoils, and the blades are oriented at apredetermined stagger for moving air in direction 122 through thepassage formed by two adjacent blades 104 as they rotate in thedirection 124 indicated by the curved black arrow. Within each casingbody 113 shown, channel 130A is formed in respective casing walls 112.

More specifically with regard to FIG. 1A, multiple circumferentialchannels 130A are formed in casing wall 112A. Circumferential casingtreatment channels are suggested in at least U.S. Pat. No. 4,239,452 toRoberts, Dec. 16, 1980; U.S. Pat. No. 4,466,772 to Okapuu, Aug. 21,1984; U.S. Pat. No. 6,527,509 to Kurokawa, Mar. 4, 2003; and U.S. Pat.No. 6,582,189 to Irie, Jun. 24, 2003, which are incorporated byreference herein in their entireties. As depicted, each ofcircumferential channels 130A forms a continuous curvilinearcross-sectional channel about inner casing wall 112A. However, thecross-sectional shape may also be square, triangular, rectangular,trapezoidal or some combination of the above (not shown). Generally, thechannels are equally spaced across the axial dimension of casing 113.Often, circumferential channels 130A are positioned in the forwardportion of blade tip 106 and terminate before reaching the rear(downstream) portion of blade tip 106. Because the cross-section isinvariant with the direction of rotation, circumferential grooves appearstationary to a moving blade and provide an increased leakage path overthe blade tip. Due to the complexity of the interaction of the flowthrough the grooves and the tip leakage, some benefit in pressure risemay be obtained for compressors, although this is generally associatedwith a decrease in efficiency.

FIG. 1B show multiple axial channels 130B fashioned radially withincasing wall 112B. Axial casing treatment channels are suggested in atleast U.S. Pat. No. 4,239,452 to Roberts, Dec. 16, 1980; U.S. Pat. No.6,540,482 to Irie, Apr. 1, 2003; and U.S. Pat. No. 6,582,189 to Irie,Jun. 24, 2003, which are incorporated by reference herein in theirentireties. Channels 130B are depicted as being square, or trapezoidal,but may instead have a curvilinear or triangular cross-sectional shape(not shown). Trapezoidal shaped channels may be highly exaggerated,wherein a portion of the depth of the channel lies radially behind thecasing wall 112B (not shown). As in the example above, axial channels130B are often positioned in the forward portion of blade tip 106 (theupstream side) and terminate before reaching the rear portion of bladetip 106 (the downstream side). An effect of the cross-section changingabruptly with the direction of rotation is to impart high tangentialmomentum in the fluid in the frame of reference of the blade. Thegrooves also provide a pathway to recirculate flow from downstream toupstream which reduces the overall efficiency of the machine.

FIG. 1C shows multiple recessed channels (or passages) 130C formedwithin casing body 113B with only ports 131C being exposed in casingwall 112B. Recessed channel casing treatment (and exposed portconfigurations) is suggested in at least U.S. Pat. No. 5,282,718 toKoff, Feb. 1, 1994; U.S. Pat. No. 5,308,225 to Koff, May 3, 1994; andU.S. Pat. No. 6,231,301 to Barnett, May 15, 2001; U.S. Pat. No.6,585,479 to Torrance Jul. 1, 2003; U.S. Pat. No. 6,736,594 to Irie May18, 2004; and U.S. Pat. No. 6,742,983, Schmuecker, Jun. 1, 2004, whichare incorporated by reference herein in their entireties. Recessedchannels 130C typically have curvilinear or oval cross-sectional shape,but may instead have a rectangular cross-sectional shape (not shown). Asdepicted, each of ports 131C are positioned radially within casing wall112C and equally spaced from each other. Port ends 131C for a particularrecess channel are generally aligned axially. However, recessed channels130C are not always aligned axially. Passages, channels and cavities(with or without turning vanes) recirculate flow from downstream, whichresults in a corresponding loss in efficiency.

Additionally, and not shown, a honeycomb structure may be formed intothe casing wall proximate to the blade tips as suggest by is suggestedin at least U.S. Pat. No. 5,520,508 to Khalid, Dec. 5, 1994. However,the honeycomb configuration time-varies pressurizing and aspirating ofcells imparts undesirable radial fluid momentum.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a casing treatment for reducing theadverse effects of tip leakage over a blade in a turbomachine. Aturbomachine is provided having at least one row of blades oriented at apredetermined stagger. Casing grooves are provided proximate to at leasta portion of the tip of the blades. The grooves are orientatedsubstantially normal to the stagger of the blades. The normal of theblade is determined from a chord of the blade. The chord may be takenacross a pair of corresponding points, one toward the upstream end andthe other toward the downstream end of the blade, hence across theextent of the cross-sectional shape of the blade. Alternatively, a bladechord may be determined over only a portion of the blade, for instancefrom a point along the centerline of the upstream end of the blade to asecond point on the centerline midway down the blade from the upstreamend. The spacing between grooves can be optimized for blade stagger inorder to find an optimal number of grooves that concurrently cross theblade. Additionally, obtaining an optimal groove depth for a particularturbomachine requires knowing only the tip clearance gap as groove depthis directly related to the tip clearance. Furthermore, since the groovemay be substantially smaller than prior art casing treatments, flowrecirculation within the groove is reduced. The blade-normal groove maytake a variety of cross-sectional shapes. Optimally, the aft-facingsurface of the groove will have less than a 45° incline to the radial atthat point.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The novel features believed characteristic of the present invention areset forth in the appended claims. The invention itself, however, as wellas a preferred mode of use, further objectives and advantages thereof,will be best understood by reference to the following detaileddescription of an illustrative embodiment when read in conjunction withthe accompanying drawings wherein:

FIGS. 1A, 1B and 1C are diagrams of a portion of blade and casing wallwith circumferential, axial and recessed casing treatments as known inthe prior art;

FIG. 2A is a cross-sectional view of an exemplary turbomachine asunderstood in the prior art;

FIG. 2B is an oblique view of a typical hub and a partial blade assemblyas known in the prior art;

FIG. 3A is a diagram depicting a blade-normal groove with respect to thechord of the blade in accordance with an exemplary embodiment of thepresent invention;

FIG. 3B is a diagram depicting a blade-normal groove with respect to thecenterline of the blade in accordance with another exemplary embodimentof the present invention;

FIGS. 4A-4D are views of a turbomachine with blade-normal casingtreatments in accordance with an exemplary embodiment of the presentinvention;

FIG. 5 is a diagram depicting the ends of a blade-normal grooves asbeing tapered in accordance with an exemplary embodiment of the presentinvention;

FIGS. 6A-6E are diagrams of various cross-sectional shapes in accordancewith exemplary embodiments of the present invention;

FIG. 7 is a cross-sectional view of a saw-toothed shape embodiment withmomentum components;

FIGS. 8A and 8B are diagrams depicting a blade-normal groove withrespect to the chord of the blade in a highly cambered turbine bladeapplication in accordance with an exemplary embodiment of the presentinvention;

FIG. 9 is a cross-sectional view of an exemplary turbomachine havingmultiple sets of casing groove and multiple sets of vane normal hubgrooves in accordance with an exemplary embodiment of the presentinvention; and

FIGS. 10A and 10B illustrate the application of the present blade-normalgroove on a mixed flow (both axial and radial flow) or radial flowturbomachine in accordance with an exemplary embodiment of the presentinvention.

Other features of the present invention will be apparent from theaccompanying drawings and from the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION Element Reference NumberDesignations

-   02: Hub surface-   03: Hub body-   04: Blade-rotating hub-mounted blade-   06: Tip of rotating blade-   08: Blade surface facing rotation direction-   09: Blade surface facing opposite rotation direction-   10: Gap (clearance) between tip of rotating hub-mounted blade-   12: Casing wall-   13: Casing body-   14: Vane (blade)—stationary casing mounted-   16: Tip of stationary vane-   18: Forward facing surface of stationary vane-   19: Aft facing surface of stationary vane-   20: Leakage flow over blade tip from high pressure side (pressure    surface) to low pressure side (suction-   22: Direction of incoming flow-   24: Rotation direction-   26: Upstream limit of blade-   28: Downstream limit of blade-   30: Groove in stationary casing wall-   31: Groove start-   32: Groove peak-   33: Groove end-   40: Groove in rotating hub surface-   50: Normal to blade-   52: Chord line of airfoil-   54: Centerline of blade cross-section-   56: Axis of rotation-   58: Radial axis-   59: Aft-facing surface-   γ: Inclination angle of aft-facing surface with respect to radial    direction-   α: Orientation of groove respect to the axle angle (blade-angle)-   g: Groove spacing-   s: Non-groove spacing between grooves-   g-s: Groove width-   A_(w): Width of airfoil-   A_(s): Axial span of airfoil-   G_(s): Axial span of grooves

Tip leakage occurs when fluid (gas or liquid) from the high pressuresides of blades leak circumferentially around the tips of the blades tothe low pressure sides, resulting in a corresponding decrease inefficiency of the turbomachine. The phenomena may be better understoodwith reference to FIGS. 2A and 2B. FIG. 2A is a cross-sectional view ofan exemplary turbomachine, while FIG. 2B is an oblique view of a typicalhub and a partial blade assembly. FIGS. 2A and 2B depict an exemplaryaxial flow machine, but leakage occurs on non-axial turbomachinery in asimilar manner. Hub body 203 is shown as having rows of rotating blades204 affixed to hub surface 202, each of which rotate on hub 203 withincasing body (or shroud) 213. Clearance gap 210 is formed between bladetips 206 and casing wall 212. In a similar configuration, stationaryvanes 214 are affixed to casing wall 212 and extend toward hub surface202, forming clearance gap 210 between vane tips 216 and hub surface202.

Leakage flow 220 escapes from high pressure sides 228 of the airfoils,circumferentially around blade tips 206 (of blades 204), to suctionsides 226 of the airfoils, or alternatively, circumferentially aroundvane tips 216 (of vanes 214). The amount of leakage 220 depends onseveral design factors for the turbomachine including airfoil design(comprising blade surfaces facing rotation direction 208, surfacesfacing opposite rotation direction 209 and vane surfaces) and themagnitude of clearance gap 220, but also depends on other operatingparameters for the machine such as the recitation speed of the hub andtemperature. Common fluid dynamic casing treatment to amelioratedetrimental effects of tip leakage include casing treatments forrecirculating fluid from the downstream part of the blade passage toupstream to energize the flow near the casing and casing treatments forbreaking up (mix out) leakage flow. Often, these improve one aspect,e.g., pressure rise, at expense of another, e.g., efficiency. Forinstance, recirculation of the fluid results in losses and reducedefficiency. Relative motion of axial grooves does not impart an axialmomentum component to the fluid and hence omits an important componentof the streamwise momentum. Injected radial momentum is not recoveredand therefore reduces efficiency of the turbomachine. Moreover, many ofthese solutions involve substantial casing modification, design work andadded weight to the turbomachine; deep slots, cavities and channels addweight and complexity to the casing. What is needed is a mechanism forimparting streamwise momentum component to the fluid with sufficientradial momentum to induce mixing with the leakage flow, but withprimarily streamwise momentum (as defined previously) to reduce thepenalties associated with the leakage.

Traditionally, as discussed elsewhere above, casing treatments haveconcentrated on, and been referenced to the axial direction of thecasing and/or the axis of rotation. This approach has yielded moderatesuccess in solutions to other shortcomings of turbomachine design, buthas met with less success in the area of preventing tip leakage loss.What is needed is a new paradigm for approaching casing treatments forreducing the adverse effects of tip leakage.

In accordance with one exemplary embodiment of the present invention acasing treatment is presented which relates to the directionalorientation (stagger) of the rotating blades rather than being relatedto the axis of rotation of the turbomachine. Grooves are disposed withinthe casing wall that are oriented substantially normal (perpendicular)to the blade. Thus, the application of the present invention representsa new paradigm in casing treatments, that is, treating the casing withregard to the stagger of the rotating blades without regard to the axisof rotation.

Hereinafter, the terms “blade-normal” and “blade-normal direction”should be understood as the direction that is perpendicular to thenormal direction from the casing wall and simultaneously perpendicularto any contour line which lies on or between the contour of forwardfacing surface of blade tip (i.e., the surface of the airfoil facingrotation direction) and the contour of the opposite facing surface ofblade tip (i.e., the surface of the airfoil facing opposite rotationdirection). As may be appreciated, the normal to a constant radiuscasing (cylindrical casing) points radially inwardly or outwardly. For acasing having a radial variation with axial location, the casing normaldirection would point in both radial and axial directions (but nevertangential). For example, the downward normal direction from an upwardlysloping casing (increasing in radius with axial location) would pointboth radially down and axially downstream. Thus, the above definitionfor blade-normal defines that direction as parallel to the casing walland could never be interpreted as the direction normal to the tip (i.e.,upward).

For instance, the blade-normal for a particular application may be takenas perpendicular to the normal direction from the casing wall andsimultaneously perpendicular to the mean line of the blade tip, i.e., acontour line defines the midline between forward facing and the oppositefacing surfaces of blade tip. Because most airfoils have a generallycurvilinear shape, the contour lines, e.g., the mean line, will alsohave a curvilinear shape. However, the blade-normal direction may bedetermined at any one point along a contour, thereby resulting in agenerally linear casing groove. Alternatively, the magnitude of theblade-normal direction may generally correspond with the curvilinearshape of the contour, resulting in a curvilinear casing groove thatmimics the shape of the contour line it was taken from.

Therefore, and as should be well appreciated, the range orientationsthat are blade-normal is bound by using any tangent along either of thetwo airfoil surfaces.

As a practical matter and as used herein, the phrase normal (orperpendicular) to the blade means the orientation for reducing theadverse effects of leakage ±25° from the perpendicular of any tangent onthe curves where the two airfoil surfaces meet the tip. The casinggrooves are axially aligned with and proximate to at least a portion ofthe blades tips. In accordance with another exemplary embodiment of thepresent invention, a hub treatment is presented which relates to thedirectional orientation of the stationary vanes. Here, grooves aredisposed within the hub surface that are oriented substantially normal(perpendicular) to the vane chord or mean line of the stationary vanes.The hub grooves are axially aligned with and proximate to at least aportion of the vane tips. The concept of blade-normal grooves may bebetter understood with respect to FIGS. 3A and 3B, both of which areradial inward views of the blade and casing, i.e., viewed inward towardthe axis of rotation.

FIG. 3A is a diagram depicting a blade-normal groove with respect to thechord of the blade in accordance with an exemplary embodiment of thepresent invention. Each of rotating blades 304 is depicted in the figureas having a width A_(w) and length A_(l.); Length A_(l) translates to aaxial length of A_(s) due to the stagger of the airfoil. The tangentialdistance from blade to blade is represented as p. Blades 304 rotate indirection 324 with flow parallel to the blade surface in the referenceframe of the blade passage 322, resulting in leakage 320 over the bladetips (also viewed in the blade frame of reference). From the top view itcan be seen that each blade has surface facing rotation direction 308and surface facing opposite rotation direction 309 which together definethe cross-sectional shape of the airfoil. Using the cross-sectionalshape, the centerline of the airfoil can be visualized as mean or camberline 354. The camber line, as is well known in the art, is a measure ofthe curvature of an airfoil and as such is an imaginary line which lieshalfway between the forward facing surface and the opposite facingsurface of the airfoil. Generally, the camber line intersects the chordline at the leading and trailing edges of the airfoil. Because mostairfoils are curvilinear, the resulting blade camber line 354 is alsononlinear.

Blade chord line 352 is depicted as a line segment passing through twocenter points of the blade along camber line 354. As shown, the centerpoints are located on the extreme upstream and downstream ends of camberline 354 (i.e., having an axial spacing of approximately A_(s)).Blade-normal 350 c is determined from blade chord 352, which thenapproximates the blade-normal based on the position of camber line 354to the blade. This blade-normal is the basis for determining theorientation angle, α, of the casing grooves measured with respect to aline parallel to the axis of rotation, represented as line 356. Inaccordance with this embodiment, one blade-normal is produced from theextent of the entire cross-sectional shape of the blade resulting in andlinear casing groove treatment oriented at angle α, with respect to theaxis of rotation of the turbomachine. As depicted in the figure,plurality of blade-normal casing grooves 330A is disposed within thecasing wall, each oriented at blade-normal angle α. Grooves 330A arespaced at a groove distance, g, with non-groove distance, s, betweengrooves (resulting in a groove width of g-s). Each of grooves 330A havean axial length of G_(s), where 0.5 A_(s)<G_(s)≦A_(s). Using the bladeto blade distance, p, optimal values for groove distance g, non-groovedistance s and groove width (g-s) may be determined as will be discussedbelow with regard to FIG. 7.

The present casing groove design imparts streamwise (i.e., parallel tothe blade surface) momentum to the leakage flow in the relative frame ofthe blade, hence reducing the adverse effects of leakage. In the bladeframe of reference, the cross-section of presently described casinggrooves 330A “moves” downstream relative to blades 304. By contrast,prior art circumferential grooves have a cross-section that appears“stationary” relative to a moving blade. The relative wall motion ofcasing grooves 330A imparts both axial and tangential momentum in thefluid via relative wall motion. Since the primary effect of a movingwall on neighboring fluid is in the direction normal to its surfacerather than parallel to it, the “motion” of the substantiallyperpendicular grooves 330A results in near-casing fluid being draggedwith wall motion and predominantly pushed normal to grooves 330A andalong (substantially parallel to) the blade stagger. Hence, theblade-normal groove orientation of the present invention impartsstreamwise momentum to the flow.

In accordance with another exemplary embodiment of the presentinvention, the blade chord used for determining the blade-normaldirection is computed over the axial portion of the blade that iscoextensive with the grooves. The portion of the blade not coextensivewith the groove is not used for chord determination. For instance, ifthe axial length, G_(s), of grooves 330A is shorter than the axial span,A_(s), of blade 304, only the G_(s)—long portion of blade 304 that iscoextensive with axial length span of grooves 330A is used for computingthe blade chord. In other words, a blade chord is defined as having bothendpoints within G_(s) (not shown). That chord is used for findingblade-normal 350-c. Blades-normal grooves 330A are then limited to anaxial length of G_(s).

By way of an another example, one chord endpoint is positioned proximateto the upstream end of the blade, for instance on camber line 354, whilethe second end of the blade chord line is located at a point on theblade corresponding to distance≧0.5 A_(l) from the first point. Thesecond point would then be positioned between the axial midpoint ofblade 304 and the downstream end of blade 304 (i.e., having an axialspacing of between 0.5 A_(s) and A_(s)), for instance also along camberline 354. The normal of that chord line is assumed to be the effectiveblade-normal for the portion of blade 304 between the chord endpointsand blade-normal grooves 330A are aligned with that blade chord.

In the preceding the blade chord was defined from endpoints along thecenter line of blade 304, i.e., camber line 354. However, in accordancewith still another exemplary embodiment of the present invention, theendpoints of a blade chord are positioned along the blade surface facingrotation direction 308 (depicted as line 308 from a radial view) oralternative along blade surface facing opposite rotation direction 309illustrated as line 309 from the radial view. In so doing, a normaltaken from this blade chord more accurately represents the normal of anairfoil surface of the blade, rather than a normal for the entirecross-sectional shape of blade 304. As will be understood from thefollowing description, the optimal area for axial coverage area for theblade-normal casing grooves of the present invention is coextensive withthe upstream half of the blades, i.e., between the upstream end of theblades and the axial midpoint of the blades (i.e., approximately 0.5A_(s) from the upstream blade end). Therefore, for optimal flow resultsthe position of the blade chord should relate to only that portion ofthe blade proximate to the casing grooves. For example, if the axiallength of blade-normal grooves is half of the axial length of theblades, G_(s)=0.5 A_(s), then the normal angle α should be determinedfrom a chord in the 0.5 A_(s) of the blade proximate to the intendedposition of the blade-normal grooves. For a compressor or pump, bytruncating the chord to the upstream portion of the blade, the magnitudeof angle α will be somewhat higher. For a turbine blade (for which thecamber angle increases with axial distance), limiting the extent of thegrooves to the upstream portion of the passage would result in lowerangle α.

FIG. 3B is a diagram depicting a blade-normal channel with respect tothe centerline of the blade in accordance with another exemplaryembodiment of the present invention. Here the blade-normal is takenalong the non-linear camber line 354 rather than the linear blade chord352. Because camber line 354 is nonlinear, a plurality of blade-normallines 350-1, 350-2 . . . 350-m result from tangential points alongcamber line 354. Thus, rather than determining a single blade-normalangle α, normal lines 350-1, 350-2 . . . 350-m result in multipleblade-normal angles α₁, α₂ . . . α_(m). Blade-normal casing grooves 330Bconstructed from normal lines 350-1, 350-2 . . . 350-m replicates thecharacter of camber line 354 as depicted in the figure. Blade-normalcasing grooves 330B represent influences on the fluid flow attributableto both sides of the airfoil equally, i.e., surface facing rotationdirection 308 and surface facing opposite rotation direction 309equally, because centerline 354 is an unweighted average of bothsurfaces. Alternatively, the line for computing the blade-normals may bebiased away from the centerline by weighting the average to shift theline away from the center position of blade 304. In accordance withstill another exemplary embodiment of the present invention, theorientation and non-linear character of blade-normal casing grooves maybe determined by the character of only one blade surface, e.g., eithersurface facing rotation direction 308 or surface facing oppositerotation direction 309, rather than the centerline of blade 304.

FIGS. 4A-4D are views of a turbomachine with blade-normal casingtreatments in accordance with an exemplary embodiment of the presentinvention. FIG. 4A is a cross-sectional view of the upper portion of aturbomachine as seen from below and along the axis of rotation in thedownstream direction. Portions of blades 404 are illustrated withincasing body 413 wherein clearance gap 410 is formed between the bladetips and casing wall 412. The direction of rotation is shown by arrow424. A plurality of blade-normal casing grooves 430 are depictedoriented at an angle α from the axis of rotation, represented as line456. Casing grooves 430 are oriented substantially normal(perpendicular) to blade chord or mean line of blades 404 (shown as line354 in FIGS. 3A and 3B).

FIG. 4B is a cross-sectional view of the upper portion of a turbomachinealong the axis of rotation. Casing grooves 430 are radially disposedaround the entire portion of casing wall 412 proximate to blades 404.Here, the cross-sectional shape of casing grooves 430 is depicted assquare or rectangular. An enlargement of casing grooves 430 containedwithin cross-sectional box 401 is depicted in FIG. 4C. Notice, however,cross-sectional box 401 is oriented perpendicular (normal) to thedirection of grooves 430. A top view of the groove structure alongsection AA is depicted in FIG. 4D (because segment line AA is curved,the resulting section is substantially flattened with respect to thecurvature of the casing).

It should be mentioned that in comparison with prior art casingchanneling, the depth (d) and width (g-s) of the present blade-normalcasing grooves are small, but large in comparison to the roughness ofthe casing wall. As such, the ingress and egress ends of theblade-normal casing grooves have been depicted as an abrupt termination.Optimally, however, rather than an abrupt transition from casing wall513 to depth d, according to one exemplary embodiment, a gradual slopeis fashioned at one or either end of the grooves, as shown in FIG. 5.There, the ingress and egress ends of blade-normal grooves 530 terminateto the casing surface as a graduated relief, having a groove width (g-s)as discussed above and with a groove depth d. Generally, the slope ofthe relief may be determined by the groove width (g-s) such that thegroove depth d occurs at an approximate distance of 2(g-s) from thegroove end.

Furthermore, although the cross-sectional shape of the presentblade-normal grooves has been depicted as square or rectangular, othergeometric shapes are possible or even favorable. FIGS. 6A-6E arediagrams of various cross-sectional shapes in accordance withembodiments of the present invention. In each figure, casing body 613 isdepicted as being sectioned orthogonal to the axis of rotation. Grooves630A-630-E are formed in casing surface 612 as a unique geometric shape.For instance, blade-normal groove 630A is rectangular (or square),blade-normal groove 630B is trapezoidal, blade-normal groove 630C istriangular with non-groove spaces of casing surface between the grooves,blade-normal groove 630D is triangular without non-groove spaces ofcasing surface between the grooves, i.e., saw-toothed, and blade-normalgroove 630E is curvilinear, e.g., elliptical, parabolic, oval, etc.).One consideration for optimizing flow results is the inclination angle,γ, of aft-facing surface with respect to radial direction discussedbelow with regard to FIG. 7. The cross-sectional shape of grooves 630should be designed such that angle γ≧0°.

As discussed elsewhere above, the turbomachine for which grooves areapplied is taken to be an axial flow type. The blade-normal grooves ofthe present invention reduce the adverse effects of leakage in othertypes of turbomachine that do not rely on axial flow. It should beappreciated that although somewhat more difficult, it is possible todetermine the chord of blade on non-axial turbomachinery. However,because the curvature of the vanes of an impeller is usually morepronounced than that of axial flow type turbomachinery, the blade-normalfor determining groove orientation is more accurately determined fromthe a line on the vane rather than its chord, e.g., a centerline. Asdescribed above, the term “blade-normal” rather than “chord-normal” toencompass both axial and non-axial types of turbomachinery.

Below is a discussion of optimizing the blade-normal grooveconfigurations based on various design parameters for turbomachines. Theoptimization will be discussed with respect to a cross-sectional vieworiented normal to the casing grooves as illustrated in FIG. 7. Itshould be appreciated, however, that although the shape is triangular,the discussion is valid for any other shape. The principles describedbelow also apply to turbomachines with large radius changes, but theparametric description of these machines is more complicated. Those ofordinary skill in the art will understand the differences and readilyapply the necessary conversions. Also, it should be understood that theparameters shown in FIG. 7 are viewed along the groove (i.e., along theorientation angle α) and that for simplicity of discussion theorientation angle α is taken to be constant along the groove.

Initially, it is possible to determine an optimal number of grooves fora particular rotor blade configuration. The number of grooves comes fromfirst determining the groove cross-section dimensions (i.e., grooveshape viewed along the groove) and the orientation angle of the grooves,α. The number of grooves can be characterized by the number of groovesper blade passage width p (tangential distance from one blade to thenext), represented below as n.

$\begin{matrix}{n = \frac{p\; \cos \; \alpha}{g}} & (1)\end{matrix}$

-   -   g=distance from groove to groove viewed along groove;    -   p=tangential distance from blade to blade;    -   n=number of grooves per blade passage width;    -   a=orientation angle of grooves

Thus, the optimal number of grooves for a given blade design comes fromobtaining optimal orientation angle α and groove cross-section widthg.

The motion of the blades with respect to the casing can be viewed fromthe rotating blade frame of reference as the casing “moving” in thedirection opposite blade rotation. For relatively smooth groovesurfaces, the motion imparted to nearby fluid is predominantly normal,or orthogonal, to the groove surfaces. To fully define the orientationof the groove aft-facing surface, define another angle as theinclination angle of groove aft-facing surface 759 with respect to aradial line 758. For rectangular groove cross-section, γ=0°. For asaw-toothed cross-section, γ<45°.

As the groove moves at speed U (radius multiplied by blade angularspeed) in the tangential direction relative to the blade, thecross-section viewed along the groove moves at speed U cos(α) in thedirection normal to the groove. Assuming that the velocity imparted tothe fluid attains a velocity normal to the aft-facing surface, itsvelocity magnitude relative to the blade can be represented as thefollowing.

U cosαcosγ  (2)

This velocity has the following components: U cosαcosγsinγ in the radialdirection; and U cosα(cosγ)² in the non-radial directions.

For an axial turbomachine envisioned in this discussion, the radialcomponent enhances mixing with the leakage flow, but does not impartbeneficial streamwise momentum. The non-radial component has the benefitof improving the streamwise momentum of the leakage flow. The directionconsiderations below reveal how α and γ should be set.

To favorably influence tip leakage flow, both the magnitude anddirection of the velocity from the grooves are important. Setting angleα for blade-normal orientation provides the optimal axial and tangentialcomponents, but some radial component is also beneficial to encouragethe groove flow to mix with the tip leakage flow. Thus, even thoughinclining the aft-facing groove surface will reduce the magnitude ofstreamwise velocity from the grooves, aft-facing groove side inclinationangle y should be set large enough to direct the groove flow toward theblade tip.

To determine the number of grooves, the size of the grooves should firstbe determined. Using d=groove depth and s=non-groove distance betweengrooves, the dimension of remaining sides of the cross-sectionparameters can be set by choosing a triangular cross-section and settingthe angle that the top groove surface makes with the aft-facing surfaceto be 90°. With such an angle, the top wall is parallel to the flow fromthe aft-facing surface.

From trigonometry, the length of the cross-section opening to the bladepassage can be determined as follows.

$\begin{matrix}\frac{d}{\cos \; \gamma \; \sin \; \gamma} & (3)\end{matrix}$

In general, some non-grooved areas can be included between grooves toimprove robustness to blade rub. The groove-to-groove distance (viewedalong the groove) is then determined as follows.,

$\begin{matrix}{g = {s + \frac{d}{\cos \; \gamma \; \sin \; \gamma}}} & (4)\end{matrix}$

Substituting into Equation (1) above, n is determined as follows.

$\begin{matrix}{n = \frac{p\; \cos \; \alpha}{s + \left( \frac{d}{\cos \; \gamma \; \sin \; \gamma} \right)}} & (5)\end{matrix}$

The above expressions for g and n apply for a triangular cross-sectionin which the angle between surfaces at the top of the groove is 90°.They illustrate how the number of grooves per blade passage widthdepends on the orientation angle α and the groove cross-section(including non-grooved space between grooves).

Next, to reduce the adverse effects of leakage, the streamwise momentumimparted to the leakage flow should be optimized. A rear-facing step (γless than 45°) with respect to the flow relative to the blade is areasonable choice for groove cross-section. The length that primarilysets the amount of leakage for a given blade design and operating pointis the tip clearance gap t. To influence the leakage flow, the groovesshould be of similar size. Thus, to provide sufficient momentum(velocity multiplied by mass flow) to alter the leakage flow, the groovedepth d should approximately equal the tip clearance gap t. Using adepth d>>t encourages recirculation of flow within blade-normal groove730 and contributes to unnecessary losses.

The following illustrates a groove design, including a suitable numberof grooves, for a saw-toothed (triangular) cross-section, where d=t andγ=30°.

Viewing the groove cross-section along the groove, the length of theaft-facing surface of the groove is

$\frac{d}{\cos \; \gamma} = {\frac{t}{0.75^{2}} = {\frac{2t}{\sqrt{3}}.}}$

The angle that the other surface makes with respect to the aft-facingsurface should be 90° so that it is parallel to the desired relativeflow direction. This results in a groove width of 4t/√{square root over(3)}.

To maximize the effect to the cross-sectional shape on leakage, a sharp“peak” should separate each groove. However, in an effort to make thegrooves more robust to blade rub, a non-grooved distance can be insertedbetween grooves, where s>0, thereby increasing the groove-to-groovedistance

The number of grooves per blade passage would then be as given byEquation 5.

$\quad\begin{matrix}{n = \frac{p\; \cos \; \alpha}{g}} \\{= \frac{p\; \cos \; \alpha}{s + \left( \frac{4t}{\sqrt{3}} \right)}}\end{matrix}$

For p=2, α=45°, t=0.1, and s=0 (p and t in arbitrary length units), nwould be approximately 6.1.

Thus, for grooves having depth equal to the clearance gap, the optimumnumber of grooves decreases with increased clearance height. Fornon-grooved space of zero, the number of grooves is inverselyproportional to clearance height.

A triangular cross-section with a non-grooved space (defined by s) wouldtherefore be more effective at imparting streamwise momentum than atrapezoidal shape. This is because a triangular shape provides an uppersurface that can be set to be parallel to the flow normal to theaft-facing surface. The trapezoidal cross-section would likely interferewith the flow normal to the aft-facing surface of the groove. Also, theadded groove cross-sectional area would increase the recirculation offlow within the groove, thereby increasing loss.

It should be reiterated that the orientation of the casing grooves mayvary with the axial location of the grooves. Thus, the local grooveorientation may be optimized by axial location. The optimal orientationangle of the groove may depart from normal to the blade angle for tworeasons: (1) blade angle variation with axial location, and (2) behaviorof leakage flow may justify a somewhat different angle fromblade-normal.

FIGS. 8A and 8B illustrates the application of the present blade-normalgroove casing treatment to an axial turbine. FIG. 8A is a top view ofthe groove structure which further depict high camber blades. The viewis radially inward toward the axis of rotation as in FIGS. 3A and 3B.Here, each of highly cambered blades 804 is depicted in the figure ashaving a width A_(w) and length A_(l.); Length A_(l) translates to aaxial length of A_(s) due to the stagger of the airfoil. The tangentialdistance from blade to blade is represented as p. Blades 804 rotate indirection 824 with flow parallel to the blade surface in the referenceframe of the blade passage 822, resulting in leakage over the bladetips. From the top view it can be seen that each blade has surfacefacing rotation direction 808 and surface facing opposite rotationdirection 809 which together define the cross-sectional shape of theairfoil. Using the cross-sectional shape, camber line 854 can be seen.Casing grooves 830 are depicted as being curvilinear that approximate ormimic the character of camber line 854. Here, casing grooves 830 aredepicted as being triangular, with groove start 831, groove peak 832 andgroove end 833, that is the groove start for the adjacent groove. Sincea turbine blade is typically more highly cambered (has more flowturning) than an axial compressor used in previous illustrations, anoptimal groove design will have varying orientation angle with axiallocation as shown. FIG. 8B is a cross-sectional view of the upperportion of the axial turbine along the axis of rotation taken at segmentline AA. The triangular shape of grooves 830 is more apparent in thecross-sectional view although, again, the cross-sectional shape of thegroove is predicated on the orientation to the groove (this view istaken perpendicular to the rotational axis and on any portion of thegrooves). Here, groove start 831, groove peak 832 and groove end 833 areclearly distinguishable. Note that the variation in orientation angle αwith axial location implies a variation in groove-to-groove distance(g-s) viewed along the groove. This is accomplished by varying either gor s, or both (not shown).

Furthermore, it should be understood that the configuration of theparticular blade-normal grooves may depend on other factors such as thedynamics of the particular stage of the turbomachine to be considered,whether the application is on the case (static) or the hub (rotation).This is graphically represented in FIG. 9. It should be understood thatthe illustration is FIG. 9 is merely exemplary and the particular casingand hub configurations are depicted by way of example only. FIG. 9 issimilar to FIG. 2B above and as such is a cross-sectional view of anexemplary turbomachine. Hub body 903 is shown as having rows of rotatingblades 904 affixed to hub surface 902, each of which rotate on hub 903within casing body 913. Blade-normal casing grooves 930A are depicted onthe first stage as having a rectangular cross-sectional shape, while inthe second stage blade-normal casing grooves 930D are shown as having atriangular cross-sectional shape without a groove space, i.e., s=0.Clearance gap 910 is shown between blade tips 906 and casing wall 912.

In accordance with still another exemplary embodiment of the presentinvention, blade (vane) normal grooves may also be disposed on hubsurface 902, such as for cantilevered stators. There, stationary vanes(stator blades) 914 are affixed to casing wall 912 and extend toward hubsurface 902, forming clearance gap 910 between vane tips 916 and hubsurface 902. Leakage may also occur across vane tips 916, as well asblade tip 906. Vane-normal hub grooves 940A are depicted on the firststage as having a rectangular cross-sectional shape, while in thesecond-stage vane normal hub grooves 940D are shown as having atriangular cross-sectional shape without a groove space, i.e., s=0.

In any case, the groove depth should be optimized for streamwise flow inthe tip region, while avoiding losses due to recirculation. As athreshold proposition, the groove depth approximately equals to the tipclearance height will satisfy both, i.e., d≈t).

As described immediately above, a good cross-sectional shape providesthe proper direction without excessive groove cross-sectional area. Thedurability benefits of rectangular or trapezoidal grooves could beobtained by adding non-grooved space s between triangular grooves. Assuch, triangular cross-sections exhibit the promise to be more effectiveand potentially just as durable. When blade rub is not a concern (e.g.,for large clearances), sharp groove peaks (s=0) are an optimal choice.

Finally, and as mentioned elsewhere above, the orientation of theblade-normal groove is an approximation of the blade-normal and variesbased on several factors such as which algorithm is used for computingthe normal. Additional, the orientation of the grooves may vary fromblade-normal without sacrificing efficiency. Assuming it is desirous tomaintain the relative streamwise velocity component within 10% on anoptimal value, the groove orientation should be maintained within ±25°of blade-normal direction. It is reiterated that the inclination angle γof the aft-facing surface of the groove should be less than 45° (i.e.,y<45°) to achieve a balance of streamwise and radial momentumcomponents.

The illustrations and discussions above have largely admitted an axialcompressor, however the present invention is equally applicable to allother types of turbomachinery with tip clearance, for example fans,blowers, pumps, turbines.

FIGS. 10A and 10B illustrate the application of the present blade-normalgroove on a mixed flow (both axial and radial flow) or radial flowturbomachine in accordance with another exemplary embodiment of thepresent invention. FIG. 10A depicts an exploded view of a radial machinewhile FIG. 10B show grooves 1030 from a bottom view with an outline ofrotor 1013 in position.

For mixed flow or radial flow pump impeller 1003, flow starts axial andbecomes largely radial in direction. Impeller blades 1004, or vanes,form complex three-dimensional shape. Grooves 1030 in casing 1013 areshown substantially perpendicular to the blade edges parallel to casing.Thus, casing grooves 1030 form a swirl, or helical, pattern in casing1013.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

1. A turbomachine with reduced leakage penalties in pressure change and efficiency comprising: a plurality of blades, each of said plurality of blades extending substantially radially from a rotational axis and terminating in a blade tip and having a forward facing surface and an opposite facing surface which join together at an upstream extent of the blade and at a downstream extent of the blade, and each said plurality of blades having a cross-sectional shape defined between the forward facing surface and the opposite facing surface; and a casing, said casing having an inner surface surrounding the plurality of blades, and a plurality of casing grooves in said inner surface, said plurality of casing grooves being oriented in a direction normal to an orientation of the plurality of blades.
 2. The turbomachine recited in claim 1, wherein the direction normal to an orientation of the plurality of blades further comprises, a direction normal to a point on one of the forward facing surface and the opposite facing surface.
 3. The turbomachine recited in claim 1, wherein the direction normal to an orientation of the plurality of blades further comprises, a direction normal to a point on a mean line between the forward facing surface and the opposite facing surface.
 4. The turbomachine recited in claim 1, wherein the direction normal to an orientation of the plurality of blades further comprises, a direction normal to a point on a chord line which intersects a mean line defined between the forward facing surface and the opposite facing surface.
 5. The turbomachine recited in claim 2, wherein the plurality of casing grooves being substantially linear.
 6. The turbomachine recited in claim 2, wherein the plurality of casing grooves being curvilinear.
 7. The turbomachine recited in claim 2, wherein each of the plurality of casing grooves is defined by a first groove wall and a second groove wall.
 8. The turbomachine recited in claim 2, wherein a cross-sectional shape of each of the plurality of casing grooves is triangular.
 9. The turbomachine recited in claim 2, wherein a cross-sectional shape of each of the plurality of casing grooves is rectangular.
 10. The turbomachine recited in claim 2, wherein a cross-sectional shape of each of the plurality of casing grooves is trapezoidal.
 11. The turbomachine recited in claim 2, wherein each of the plurality of grooves being defined by an upstream extent and a downstream extent.
 12. The turbomachine recited in claim 11, wherein said upstream extent of the plurality of grooves is downstream from the upstream extent of the plurality of blades.
 13. The turbomachine recited in claim 12, wherein said downstream extent of the plurality of grooves is upstream from the downstream extent of the plurality of blades.
 14. The turbomachine recited in claim 1, wherein the direction normal to an orientation of the plurality of blades being between a minimum tangential angle at any point on said forward facing and opposite surfaces, and a maximum tangential angle at any other point on said forward facing and opposite facing surfaces.
 15. The turbomachine recited in claim 14, wherein each of said plurality of blades having a camber line defining blade orientation, and each of said plurality of casing grooves having a shape defined by at least a portion of said camber line.
 16. The turbomachine recited in claim 8, said casing further comprises a surface portion between each of the plurality of grooves.
 17. The turbomachine recited in claim 8, said casing further comprises a peak between each of the plurality of grooves.
 18. The turbomachine recited in claim 1 further comprises: a plurality of vanes, each of said plurality of vanes extending substantially radially from the casing and terminating in a vane tip and having a forward facing surface and an opposite facing surface which join together at an upstream extent of the blade and at a downstream extent of the vane, and each said plurality of vanes having a cross-sectional shape defined by the forward facing surface and the opposite facing surface; a hub, said hub having an outer surface, said outer surface adjoining the plurality of blades; and a plurality of hub grooves within the hub surface, said plurality of hub grooves being oriented in a direction normal to the plurality of vanes.
 19. The turbomachine recited in claim 1, wherein the turbomachine is one of an axial flow machine and a non axial flow machine.
 20. The turbomachine recited in claim 1, wherein the turbomachine is one of a turbine, compressor, fan, blower and pump. 